[libc++] Allow detecting whether the executor supports Bash

[ldionne]

Summary

A few tests in the test suite require support for Bash. For example,
tests that run a program and send data through stdin to it require some
way of piping the data in, and we use a Bash script for that.

However, some executors (e.g. an embedded systems simulator) do not
support Bash, so these tests will fail. This commit adds a Lit feature
that tries to detect whether Bash is available through conventional
means, and disables the tests that require it otherwise.

[ldionne]

Rebase onto main

libcxx/test/std/input.output/iostream.objects/narrow.stream.objects/cerr.sh.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // <iostream>
 
 // istream cerr;
 
 // XFAIL: LIBCXX-WINDOWS-FIXME
 
+// UNSUPPORTED: executor-has-no-bash
 // FILE_DEPENDENCIES: ../check-stderr.sh
 // RUN: %{build}
 // RUN: %{exec} bash check-stderr.sh "%t.exe" "1234"
 
 #include <iostream>
 #include <cassert>
 
 #include "test_macros.h"
 
 int main(int, char**) {
     std::cerr << "1234";
     assert(std::cerr.flags() & std::ios_base::unitbuf);
     assert(std::cerr.tie() == &std::cout);
     return 0;
 }

libcxx/test/std/input.output/iostream.objects/narrow.stream.objects/cin.sh.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // <iostream>
 
 // istream cin;
 
+// UNSUPPORTED: executor-has-no-bash
 // FILE_DEPENDENCIES: ../send-stdin.sh
 // RUN: %{build}
 // RUN: %{exec} bash send-stdin.sh "%t.exe" "1234"
 
 #include <iostream>
 #include <cassert>
 
 int main(int, char**) {
     int i;
     std::cin >> i;
     assert(i == 1234);
     return 0;
 }

libcxx/test/std/input.output/iostream.objects/narrow.stream.objects/clog.sh.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // <iostream>
 
 // istream clog;
 
 // XFAIL: LIBCXX-WINDOWS-FIXME
 
+// UNSUPPORTED: executor-has-no-bash
 // FILE_DEPENDENCIES: ../check-stderr.sh
 // RUN: %{build}
 // RUN: %{exec} bash check-stderr.sh "%t.exe" "1234"
 
 #include <iostream>
 
 int main(int, char**) {
     std::clog << "1234";
     return 0;
 }

libcxx/test/std/input.output/iostream.objects/narrow.stream.objects/cout.sh.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // <iostream>
 
 // istream cout;
 
 // XFAIL: LIBCXX-WINDOWS-FIXME
 
+// UNSUPPORTED: executor-has-no-bash
 // FILE_DEPENDENCIES: ../check-stdout.sh
 // RUN: %{build}
 // RUN: %{exec} bash check-stdout.sh "%t.exe" "1234"
 
 #include <iostream>
 
 int main(int, char**) {
     std::cout << "1234";
     return 0;
 }

libcxx/test/std/input.output/iostream.objects/wide.stream.objects/wcerr.sh.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // <iostream>
 
 // istream wcerr;
 
 // XFAIL: libcpp-has-no-wide-characters
 // XFAIL: LIBCXX-WINDOWS-FIXME
 
+// UNSUPPORTED: executor-has-no-bash
 // FILE_DEPENDENCIES: ../check-stderr.sh
 // RUN: %{build}
 // RUN: %{exec} bash check-stderr.sh "%t.exe" "1234"
 
 #include <iostream>
 #include <cassert>
 
 #include "test_macros.h"
 
 int main(int, char**) {
     std::wcerr << L"1234";
     assert(std::wcerr.flags() & std::ios_base::unitbuf);
     assert(std::wcerr.tie() == &std::wcout);
     return 0;
 }

libcxx/test/std/input.output/iostream.objects/wide.stream.objects/wcin.sh.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // <iostream>
 
 // istream wcin;
 
 // XFAIL: libcpp-has-no-wide-characters
 
+// UNSUPPORTED: executor-has-no-bash
 // FILE_DEPENDENCIES: ../send-stdin.sh
 // RUN: %{build}
 // RUN: %{exec} bash send-stdin.sh "%t.exe" "1234"
 
 #include <iostream>
 #include <cassert>
 
 int main(int, char**) {
     int i;
     std::wcin >> i;
     assert(i == 1234);
     return 0;
 }

libcxx/test/std/input.output/iostream.objects/wide.stream.objects/wclog.sh.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // <iostream>
 
 // istream wclog;
 
 // XFAIL: libcpp-has-no-wide-characters
 // XFAIL: LIBCXX-WINDOWS-FIXME
 
+// UNSUPPORTED: executor-has-no-bash
 // FILE_DEPENDENCIES: ../check-stderr.sh
 // RUN: %{build}
 // RUN: %{exec} bash check-stderr.sh "%t.exe" "1234"
 
 #include <iostream>
 
 int main(int, char**) {
     std::wclog << L"1234";
     return 0;
 }

libcxx/test/std/input.output/iostream.objects/wide.stream.objects/wcout.sh.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // <iostream>
 
 // istream wcout;
 
 // XFAIL: libcpp-has-no-wide-characters
 // XFAIL: LIBCXX-WINDOWS-FIXME
 
+// UNSUPPORTED: executor-has-no-bash
 // FILE_DEPENDENCIES: ../check-stdout.sh
 // RUN: %{build}
 // RUN: %{exec} bash check-stdout.sh "%t.exe" "1234"
 
 #include <iostream>
 
 int main(int, char**) {
     std::wcout << L"1234";
     return 0;
 }

libcxx/utils/libcxx/test/dsl.py

def hasCompileFlag(config, flag):
   checking whether that succeeds.
   """
   with _makeConfigTest(config) as test:
     out, err, exitCode, timeoutInfo = _executeScriptInternal(test, [
       "%{{cxx}} -xc++ {} -Werror -fsyntax-only %{{flags}} %{{compile_flags}} {}".format(os.devnull, flag)
     ])
     return exitCode == 0
 
+@_memoizeExpensiveOperation(lambda c, s: (c.substitutions, c.environment, s))
+def runScriptExitCode(config, script):
+  """
+  Runs the given script as a Lit test, and returns the exit code of the execution.
+
+  The script must be a list of commands, each of which being something that
+  could appear on the right-hand-side of a `RUN:` keyword.
+  """
+  with _makeConfigTest(config) as test:
+    _, _, exitCode, _ = _executeScriptInternal(test, script)
+    return exitCode
+
 @_memoizeExpensiveOperation(lambda c, l: (c.substitutions, c.environment, l))
 def hasAnyLocale(config, locales):
   """
   Return whether the runtime execution environment supports a given locale.
   Different systems may use different names for a locale, so this function checks
   whether any of the passed locale names is supported by setlocale() and returns
   true if one of them works.
 

libcxx/utils/libcxx/test/features.py

DEFAULT_FEATURES = [
   # Note: To implement this check properly, we need to make sure that we use something inside the
   # compiled library, not only in the headers. It should be safe to assume that all implementations
   # define `operator new` in the compiled library.
   Feature(name='cant-build-shared-library',
           when=lambda cfg: not sourceBuilds(cfg, """
             void f() { new int(3); }
           """, ['-shared'])),
 
+  # Whether Bash can run on the executor.
+  # This is not always the case, for example when running on embedded systems.
+  Feature(name='executor-has-no-bash',
+          when=lambda cfg: runScriptExitCode(cfg, ['%{exec} bash --version']) != 0),
+
   Feature(name='apple-clang',                                                                                                      when=_isAppleClang),
   Feature(name=lambda cfg: 'apple-clang-{__clang_major__}'.format(**compilerMacros(cfg)),                                          when=_isAppleClang),
   Feature(name=lambda cfg: 'apple-clang-{__clang_major__}.{__clang_minor__}'.format(**compilerMacros(cfg)),                        when=_isAppleClang),
   Feature(name=lambda cfg: 'apple-clang-{__clang_major__}.{__clang_minor__}.{__clang_patchlevel__}'.format(**compilerMacros(cfg)), when=_isAppleClang),
 
   Feature(name='clang',                                                                                                            when=_isClang,
           actions=[AddCompileFlag('-D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER')]),
   Feature(name=lambda cfg: 'clang-{__clang_major__}'.format(**compilerMacros(cfg)),                                                when=_isClang),